1. Field of the Invention
The present invention relates to a gas spring which is interposed between a vehicle body and a back door or the like in a vehicle, and is preferably used for applying an assist force when opening the door.
2. Description of the Related Art
Since the back door of a vehicle is generally mounted so as to be opened and closed about a horizontal axis, a gas spring device employs an inverted type gas spring structured such that a cylinder is positioned in an upper side and a piston rod is positioned in a lower side when the back door is closed.
In the gas spring structured as mentioned above, a small amount of working fluid is injected within the cylinder for lubricating a seal lip portion of a seal member and the like. Accordingly, when the door is closed, since the working fluid moves to a side of a cylinder opening end portion so as to dip the seal lip portion, no oil film break is generated between the piston rod and the seal lip portion, so that no gas leaks to the outer side.
However, in some types of vehicles, the gas spring is used in a horizontal state. In this case, the seal lip portion of the seal member is not sufficiently dipped with the working fluid. As a result, an oil film is not formed between the seal lip portion and an outer periphery of the piston rod, and a pressurized gas leaks to the outer side of the cylinder due to a lack of seal caused by the oil film break or an abrasion in the seal lip portion.
In a gas cylinder for solving the problem mentioned above, there is a gas spring in which two seal members are provided in an opening end portion of the cylinder so as to be spaced in an axial direction, and a lubricant such as a working fluid or grease is injected between two seal members (Japanese Patent Application Laid-Open No. 2-21042 (patent publication 1)).
In the gas spring structured as mentioned above, since the lubricant such as grease or the like injected between two seal members always wets or lubricates the seal lip portion of the seal member even in the case that the gas spring is arranged in the horizontal state, the pressurized gas in the inner portion of the cylinder does not leak to the outer side.
The gas cylinder of the patent publication 1 has the following problems.
(1) A packing 4 is clamped among a piston rod guide member 5, a disc 7 and a support sleeve 8, and is fixed to a portion between an annular protruding portion 6 formed in a cylinder and a collared cylinder end portion 12. Thereafter, a pressurized gas is charged into the cylinder from an inner periphery of the packing 4.
As a result, since the gas is charged through a small annular gap between the inner periphery of the packing 4 and a piston rod 3, there is a problem that a long time is required for charging the gas, and productivity is not good.
Further, since the piston rod guide member 5 having a small annular gap is further arranged in a lower side of the packing 4, there is a problem in that the time for charging the pressured gas is further increased.
(2) After charging the pressurized gas, the lubricant is injected in an annular chamber between the support sleeve 8 and the piston rod 3, and the annular chamber is sealed with respect to the outer side by a packing 9 and a close ring 10. That is, the close ring 10 is provided in an upper portion of the packing for sealing the lubricant, and closes the opening end portion of the cylinder. As a result, in addition to the piston rod guide member 5, another piston rod guide member, that is, the close ring 10 is provided as a member for guiding the piston rod. An increase in a number of parts is caused, which becomes expensive.